James Stewart stars as a test driver for a large auto plant. He and his crew have developed a new high-speed carburetor and are determined to perfect it in time for the big race at the Indianapolis Speedway. While he's trying to work out the bugs in the new system, the owner's daughter,
Wendy Barrie, encourages him to allow her engineer friend, Weldon Heyburn, to have a look. Heyburn helps out, but soon tension develops between the two men, who both have amorous feelings for Barrie. The day comes to test the new carburetor, but the experiment nearly ends in disaster when the car
crashes, injuring driver Ted Healy and nearly asphyxiating Stewart with carbon monoxide...